It is desirable to enhance the strength of articles molded from polyethylene terephthalate glass fibers, asbestos fibers or other fibrous mineral materials with a coupling agent, in the resin. Furthermore, it is sometimes sufficient to merely increase the modulus by use of a filler, such as beads or a mineral of low aspect ratio, in the resin. However, heretofore, it was necessary to use very high mold temperatures, on the order of 130.degree. C., to obtain molded articles from such reinforced or filled resins which had a glossy surface and which were not rough in texture. If these high mold temperatures were not employed, the molded articles had a rough surface with poor gloss. It is believed that the crystallization rate of polyethylene terephthalate is too slow below about 130.degree. C. to result in a molded article having good surface characteristics.
While good surface characteristics can be obtained at molding temperatures of 130.degree. C. or more, the use of such temperatures is not practical in the molding field, for most molds are heated with water and attain temperatures of only about 85.degree.-110.degree. C.
A few molding devices employ heating means such as oil to reach temperatures higher than 85.degree.-110.degree. C. but these generally are inconvenient to use and still either do not generally reach such temperatures or reach them unevenly because of inadequate coring. Because of these heating problems, it has proven commercially unattractive to employ these high temperature molding devices with reinforced or filled polyethylene terephthalate resins.